Mongoose Embedded Web Server Library - Mongoose is more than an embedded webserver. It is a multi-protocol embedded networking library with functions including TCP, HTTP client and server, WebSocket client and server, MQTT client and broker and much more.
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README.md

Mongoose - Embedded Web Server / Embedded Networking Library

Mongoose is ideal for embedded environments. It has been designed
for connecting devices and bringing them online. On the market since 2004,
used by vast number of open source and
commercial products - it even runs on the International Space station!
Mongoose makes embedded network programming fast, robust, and easy.